It may be the world's oldest profession, but prostitution is using some 21st-century tricks.

The prostitution scandal involving New York Gov. Eliot Spitzer lays bare some of the inner workings of modern-day sex work: text messaging to clock in the client, electronic fund transfers, a Web site featuring color photos, prices and rankings.

There's always been a distinction between indoor and street-level prostitution, and advances in technology have increasingly separated the two, said Ronald Weitzer, author of "Sex for Sale: Prostitution, Pornography and the Sex Industry."

Not only can prostitutes and escort services now run more efficient businesses, but they can leverage word-of-mouth advertising in new ways to build their brands and troll for clients. Online social communities built around the escort and sex worker industries can solidify customer loyalty.

"It's commercial, but it's also social, so people do really form relationships," says Audacia Ray, author of "Naked on the Internet: Hookups, Downloads, and Cashing in on Internet Sexploration" and a former sex worker.

"Clients become buddies," she said.

There are a host of online message boards where clients or potential clients can discuss, rate and exchange information about individual women.

A recent rating of one woman on the escort-review site http://www.bigdoggie.com reads: "She is the real deal. She's bright, funny, enthusiastic, beautiful, flawless body, really loves what she does."

Another woman got a bad review — not for her physical shortcomings, but for her communications etiquette: "... didn't return calls or e-mails. Irresponsible."

Such sites are natural places for escorts or prostitutes to advertise, linking to their own Web sites, a technique many sex workers use, Ray said.

Technology also eases the business-end of things, Weitzer says. While clients are surveying potential companions, escort-service managers can look into clients with a background check or even a simple Google search.

Payment is easier, too.

"It's often convenient to have an account established with a balance, so if you have the last-minute urge, you don't have to worry about getting money into the account," says Norma Jean Almodovar, executive director of the sex workers' rights organization COYOTE ("Call Off Your Old Tired Ethics") in Southern California.

Emperors Club VIP, the high-end prostitution organization Spitzer allegedly was involved with, was brought down when banks noticed frequent cash transfers from several accounts and filed suspicious-activity reports with the Internal Revenue Service, a law enforcement official told The Associated Press.

The accounts were traced back to Spitzer, and public-corruption investigators opened an inquiry.

It's a long way from leaving cash on the dresser.

Cell phones are handy, too. According to court documents, some details of the alleged appointment Spitzer had with a prostitute were arranged via text message. She was even instructed by her home office to send a text message when he arrived so the office could start the clock ticking on his allotted time, according to court papers.

Devices such as Web cams also have created new opportunities, Almodovar said.

For instance, if a customer is traveling and wants to talk with a prostitute, "he can just go on the Internet and she can be in her home, and he can be in Europe, and they can have long-distance sexual dalliances," Almodovar said.

But even with so much electronic evidence, authorities permit a lot of prostitution to happen without repercussions.

"On the one hand, they're advertised, openly. So you know it exists, and you're letting it go. But then they're not taxed, or prosecuted, unless it becomes a quality-of-life issue or (involves) a public figure they happen to run across. Think of all that cash," said Assistant Philadelphia District Attorney Rich DeSipio, who is assigned to the sex-crimes unit.

And sex workers also can use high-tech measures to avoid getting caught.

High-end call girls might use bug- and camera-detection equipment to look for surveillance devices, said Jimmie Mesis, editor in chief of Professional Investigator Magazine.

Police often don't find the equipment until after they make an arrest, Mesis said. "They realize, 'Look at this. She has a bug detector. She has a hidden-camera detector. This is a pretty sophisticated set-up here.'"

But for every client who is revealed, no one knows how much prostitution remains hidden.

"The surprise should not be that (Spitzer) was a client, but that he got exposed," Almodovar said. "Despite the technology we have, 99 percent of them will never get discovered.